Method and device for spectral expansion for an audio signal

Abstract

A method and device for automatically increasing the spectral bandwidth of an audio signal including generating a “mapping” (or “prediction”) matrix based on the analysis of a reference wideband signal and a reference narrowband signal, the mapping matrix being a transformation matrix to predict high frequency energy from a low frequency energy envelope, generating an energy envelope analysis of an input narrowband audio signal, generating a resynthesized noise signal by processing a random noise signal with the mapping matrix and the envelope analysis, high-pass filtering the resynthesized noise signal, and summing the high-pass filtered resynthesized noise signal with the input narrowband audio signal. Other embodiments are disclosed.

What is claimed is: 
     
       1. A method for automatically expanding a spectral bandwidth of an audio signal comprising the steps of:
 a first training step of generating a mapping matrix, by a digital signal processor, the mapping matrix being a transformation matrix to predict high frequency energy from a low frequency energy envelope, the first training step consisting of simultaneously recording a sentence by an ambient microphone and by an ear canal microphone located in an earphone, wherein the ambient microphone captures a reference wideband signal and the digital signal processor performs a frequency transform on the wideband signal, wherein the ear canal microphone captures a reference narrowband signal and the digital signal processor performs a frequency transform on the narrowband signal into a plurality of bands, wherein the mapping matrix is based on an analysis of the frequency transform on the wideband signal and the frequency transform on the narrowband signal into a plurality of bands; 
 generating, by the digital signal processor, an energy envelope analysis of an input narrowband audio signal; 
 generating, by the digital signal processor, a resynthesized noise signal by processing a random noise signal with the mapping matrix and the envelope analysis; 
 high-pass filtering, by the digital signal processor, the resynthesized noise signal; and 
 summing, by the digital signal processor, the high-pass filtered resynthesized noise signal with the input narrowband audio signal to automatically expand the spectral bandwidth of the input narrowband audio signal to produce a summed signal with spectral enhancement; 
 reproducing by a loudspeaker the summed signal with spectral enhancement. 
 
     
     
       2. The method of  claim 1 , wherein the reference wideband and narrowband signals consist of a simultaneous recording of a phonetically balanced sentence. 
     
     
       3. The method of  claim 1 , where the input narrowband audio signal is taken from the ear-canal microphone within the occluded ear canal and located in the earphone. 
     
     
       4. The method of  claim 1 , where the input narrowband audio signal is taken from a received speech audio signal in a speech telecommunications system. 
     
     
       5. The method of  claim 1 , where the summed signal is directed to a speech telecommunications system. 
     
     
       6. The method of  claim 1 , where the summed signal is directed to a voice controlled device. 
     
     
       7. The method of  claim 1 , where the mapping matrix is generated from a least squares fit analysis of the reference wideband and reference narrowband signals. 
     
     
       8. The method of  claim 1 , where the mapping matrix is generated by a linear regression model, where the input reference wideband signals and reference narrowband signals are first converted to a frequency domain representation using a Fast Fourier Transform, and secondly each frequency band envelope is converted to a decibel domain representation to perform a linear prediction. 
     
     
       9. A non-transitory computer readable medium containing instructions for spectral enhancement, the execution of the instructions by one or more processors of a computer system causing the one or more processors to perform operations comprising:
 generating a mapping matrix, the mapping matrix being a transformation matrix to predict high frequency energy from a low frequency energy envelope, generating of the mapping matrix consisting of simultaneously recording of a sentence by an ambient microphone and by an ear canal microphone, wherein the ambient microphone captures a reference wideband signal and the digital signal processor performs a frequency transform on the wideband signal, wherein the ear canal microphone captures a reference narrowband signal and the digital signal processor performs a frequency transform on the narrowband signal into a plurality of bands, wherein the mapping matrix is based on an analysis of the frequency transform on the wideband signal and the frequency transform on the narrowband signal into a plurality of bands; 
 generating an energy envelope analysis of an input narrowband audio signal; 
 generating a resynthesized noise signal by processing a random noise signal with the mapping matrix and the envelope analysis; 
 high-pass filtering the resynthesized noise signal; 
 summing the high-pass filtered resynthesized noise signal with the input narrowband audio signal to produce a summed signal with spectral enhancement; and 
 reproducing by a loudspeaker the summed signal with spectral enhancement. 
 
     
     
       10. A system for automatically expanding the spectral bandwidth of an audio signal comprising:
 one or more processors; 
 a memory having instructions and being operatively coupled to the one or more processors, the instructions when executed by the one or more processors performs the operations of:
 generating a mapping matrix, consisting of simultaneously recording of a sentence by an ambient microphone and by an ear canal microphone, wherein the ambient microphone captures a reference wideband signal and the digital signal processor performs a frequency transform on the wideband signal, wherein the ear canal microphone captures a reference narrowband signal and the digital signal processor performs a frequency transform on the narrowband signal into a plurality of bands, wherein the mapping matrix is based on an analysis of the frequency transform on the wideband signal and the frequency transform on the narrowband signal into a plurality of bands; 
 generating an energy envelope analysis of an input narrowband audio signal; 
 generating a resynthesized noise signal by processing a random noise signal with the mapping matrix and the envelope analysis to provide a resynthesized noise signal; 
 high-pass filtering the resynthesized noise signal to provide a high-pass filtered resynthesized noise signal; and 
 summing the high-pass filtered resynthesized noise signal with the input narrowband audio signal to provide a wideband signal to produce a summed signal with spectral enhancement; 
 reproducing by a loudspeaker the summed signal with spectral enhancement. 
 
 
     
     
       11. The system of  claim 10 , wherein the mapping matrix is a transformation matrix predicting high frequency energy from a low frequency energy envelope. 
     
     
       12. The system of  claim 10 , wherein the summing provides the wideband signal as the output to the loudspeaker for reproducing the audio signal with an expanded spectral bandwidth. 
     
     
       13. The system of  claim 12 , where the mapping matrix is generated from a least squares fit analysis of the reference wideband signal and reference narrowband signal. 
     
     
       14. The system of  claim 12 , where the mapping matrix is generated by a linear regression model, where the input reference wideband signals and reference narrowband signals are first converted to a frequency domain representation providing frequency band envelopes, and secondly each frequency band envelope is converted to a decibel domain representation. 
     
     
       15. The system of  claim 10 , wherein the system further includes a smart watch having one or more microphones. 
     
     
       16. The system of  claim 10 , wherein the system further includes a set of smart glasses having one or more microphones. 
     
     
       17. The system of  claim 10 , wherein the system further includes a mobile phone having one or more microphones. 
     
     
       18. The system of  claim 10 , wherein the system further includes a hearing aid having one or more microphones. 
     
     
       19. The system of  claim 10 , wherein the system further includes steering wheel having one or more microphones. 
     
     
       20. The system of  claim 10 , wherein the system is formed in an earpiece device.